Effective treatment of low risk acute GVHD with itacitinib monotherapy.

The standard primary treatment for acute graft vs host disease (GVHD) requires prolonged, high dose systemic corticosteroids (SCS) that delay reconstitution of the immune system. We used validated clinical and biomarker staging criteria to identify a group of patients with low risk (LR) GVHD that is very likely to respond to SCS. We hypothesized that itacitinib, a selective JAK1 inhibitor, would effectively treat LR GVHD without SCS. We treated 70 patients with LR GVHD in a multicenter, phase 2 trial (NCT03846479) with 28 days of itacitinib 200 mg/day (responders could receive a second 28-day cycle) and compared their outcomes to 140 contemporaneous, matched control patients treated with SCS. More patients responded to itacitinib within 7 days (81% vs 66%, p=0.02) and response rates at day 28 were very high for both groups (89% vs 86%, p=0.67) with few symptomatic flares (11% vs 12%, p=0.88). Fewer itacitinib treated patients developed a serious infection within 90 days (27% vs 42%, p=0.04) due to fewer viral and fungal infections. Grade ≥3 cytopenias were similar between groups except for less severe leukopenia with itacitinib (16% vs 31%, p=0.02). No other grade ≥3 adverse events occurred in >10% of itacitinib treated patients. There were no significant differences between groups at 1-year for non-relapse mortality (4% vs 11%, p=0.21), relapse (18% vs 21%, p=0.64), chronic GVHD (28% vs 33%, p=0.33) or survival (88% vs 80%, p=0.11). Itacitinib monotherapy seems to be a safe and effective alternative to SCS treatment for LR GVHD that deserves further investigation.